An integrated circuit (IC) that includes two or more dies within a single package is referred to as a multi-die IC. One type of multi-die IC, referred to as a “stacked die IC,” is formed by stacking multiple dies. In some cases, the multi-die IC utilizes an entirely passive die, referred to as an “interposer,” to which one or more other dies are attached. The passive interposer die provides signal lines, e.g., wires, that communicatively link the various dies attached thereto.
Testing passive interposer dies is often a challenging endeavor. A passive interposer die may include thousands of wires. Under ideal circumstances, each wire would be electrically tested. For example, in-line defect inspection of wires may be performed. Within a production environment, however, time and cost significantly limit test coverage for the wires when using in-line defect inspection. As such, 100% test coverage of wires is not realistically possible.
In other cases, dummy test wires may be added to a passive die interposer for testing purposes. While dummy test wires may provide some benefits, coverage of usable wires within the passive interposer die remains an issue. Moreover, to achieve an adequate level of testing, the dummy test wires themselves may use significant area of the passive die interposer. The area occupied by the dummy test wires may significantly reduce the area available for non-dummy circuit elements that are available for use within a circuit design of a user.